Food material properties and jaw loading in wild lemurs

This project examines the variables that load the jaw during feeding and ultimately determine its shape. We will make detailed observations during all phases of feeding from initial food placement to chew counts to measurement of the mechanical properties of the diets. Food material properties (FMPs) describe the internal, structural properties of a diet, and, coupled with information on shape and size, characterize the physical interactions of foods with the anatomical structures that break them down (e.g., teeth, jaw, chewing muscles). However, experimental work has often failed to find a direct connection between FMPs and chewing structures despite the broad similarities between dietary specialization and anatomy found across mammals. We will study two wild primate species, Verreauxs sifaka and ring-tailed lemurs, that live in the same dry forest in southwestern Madagascar. Though the diets of these species overlap, their jaw forms differ. Furthermore, one of the species is a leaf eater with related anatomical specializations; they can be observed at close range; and they occur in relatively large populations. In addition, new developments in in-field testing of plant materials could lead to better characterization of diets and identification of the relevant variables that are ultimately responsible for structural differences. The proposed project will provide practical data to experimental studies since field observations will be made at each step of feeding, and relevant variables, such as chew numbers and FMPs, will be quantified. These data will be used to calculate bite forces for different foods, which contribute to daily jaw loads. We will then statistically compare biting frequencies, bite force, and daily load to FMPs. Our goal is to test the extent to which FMPs contribute to jaw loading and when these effects are felt, either during food preparation or chewing. Secondarily, we are examining how leaf eating in particular contributes to jaw form, given the diet of sifakas and the specialized anatomy it shares with other leaf eaters. We will also conduct nutritional analyses of the foods. Though nutrients do not have an obvious connection to jaw loading, their relationships to FMPs may be related to individual decisions on food selection. The novelty of our approach is in quantifying those variables specifically related to stressing the jaw, subsequent testing of the FMPs of the diet, and estimating jaw loading from field-derived variables. The primary objective is to identify the relevant variables that contribute to food choice, feeding efficiency, and, ultimately, structural adaptation. The significance of this research is that behavioral and environmental variables can potentially be predicted from anatomical structures with greater accuracy, which can be applied to analyzing fossil specimens.

This project examines the variables that load the jaw during feeding and ultimately determine its shape. We studied two wild primate species, Verreaux's sifaka and ring-tailed lemurs. Though they live in the same dry forest in southwestern Madagascar, the species differ in their jaw shapes. The species can be observed at close range and occur in high densities at the field site. One major component of our study was to describe foods in terms of their material properties. Food material properties (FMPs), such as toughness, describe the internal, structural properties of a diet, and, coupled with information on shape and size, determine the physical interactions of foods with the anatomical structures that break them down (e.g., teeth, jaw, associated muscles). Previous experimental work had often failed to find direct relationships between material properties and food processing. Behavioral observations of wild animals are necessary to accurately assess the location and amount of the loads on these structures. The novelty of our project lies in the integrated data collection throughout the feeding cycle, from measuring 1) time spent feeding on individual food parts, 2) FMPs, 3) bite and chew counts, and 4) food intake. The primary question we were investigating was whether bite/chew counts and intake were affected by food material properties. These data were collected during all-day focal follows of individual animals in dry and wet seasons to obtain dietary intake data on a daily and seasonal scale. Total daily bites and chews increased with food toughness, whereas food intake decreased with toughness. Our study confirms that the two species react differently to tough foods. The effects are greater for the ring-tailed lemurs-they adjust behaviorally when biting/chewing, which aligns with their more slender jaw. The more robust sifaka is relatively invariant in its approach to feeding. The ring-tailed lemurs also chew at a much faster rate than the sifakas, though, importantly, this does not translate into greater food intake or bite/chew numbers since the sifakas feed for a longer time per day. When considering daily and seasonal effects, both species take in less food as the food becomes more difficult to process, and bites and chews increase as foods become tougher and stiffer. The contrast between our per plant results and cumulative daily effects clearly demonstrate that the real impact of food processing can only be determined with detailed daily observations. Our study shows that FMPs, seasonality, and food shape affect food processing behaviors that impact how the jaw is loaded. As an added benefit to our study, working in a developing nation raises awareness at all levels of governance of the value of their resources and encourages participation by the local people to protect it.